What Causes Pain In Hips And Ball-like Structures In Pelvic Region?

Hi, I'm 16 years old (5 foot 8, 140 lbs) and a week and a half ago after hockey practice, i began having pain in my hips. I stretched daily before the injury and I still do. But recently i noticed that there are ball-like structures in my pelvic region on my hip flexors. Any idea what this may be, or if it is normal and unrelated to the pain?